Mac mini shutting down mysteriously

Question

Mac mini shutting down mysteriously

For a while now, my 2009 Mac mini has been shutting itself off for no apparent reason. It typically happens every few days, when I'm away from the computer.

Possible suspects include a failing AC adapter and maybe my aging Tripp-Lite UPS commanding a shutdown due to a weak battery. (Since it was new, the UPS has always done a weird thing—or maybe a self-test—once or twice a day where it apparently switches to backup power for a second or two, and the Mac pops up an alert that the power has failed, but AC mode comes right back on and this seems unrelated to the random shutdowns.)

I figure there must be a log file somewhere that will tell my why it's doing this, but I don't know where to look. Any ideas?

Mac mini, OS X Mavericks (10.9.2), 8GB RAM, running OS X Server

Posted on Jul 13, 2015 11:29 PM

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Answer 1

lllaass

Level 10

210,417 points

Jul 14, 2015 1:23 AM in response to G Robert Lewis

Note the time of the next shutdown. After rebooting open the Console app in Finder>Applications>Utilities and look for log entries at the time of the freeze. Post suspicious ones here.

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Answer 2

Linc Davis

Level 10

209,547 points

Jul 14, 2015 7:19 AM in response to G Robert Lewis

These instructions must be carried out as an administrator. If you have only one user account, you are the administrator.

This procedure is a diagnostic test. It makes no changes to your data.

Please triple-click anywhere in the line below on this page to select it:

syslog -k Sender kernel -k Message CSeq 'n Cause: -' | tail | awk '/:/{$4=""; print}' | pbcopy

Copy the selected text to the Clipboard by pressing the key combination command-C.

Launch the built-in Terminal application in any of the following ways:

☞ Enter the first few letters of its name into a Spotlight search. Select it in the results (it should be at the top.)

☞ In the Finder, select Go ▹ Utilities from the menu bar, or press the key combination shift-command-U. The application is in the folder that opens.

☞ Open LaunchPad. Click Utilities, then Terminal in the icon grid.

Paste into the Terminal window by pressing the key combination command-V. I've tested these instructions only with the Safari web browser. If you use another browser, you may have to press the return key after pasting.

Wait for a new line ending in a dollar sign ($) to appear below what you entered.

The output of the command will be automatically copied to the Clipboard. If the command produced no output, the Clipboard will be empty. Paste into a reply to this message.

The Terminal window doesn't show the output. Please don't copy anything from there.

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Answer 3

Jul 14, 2015 9:46 AM in response to lllaass

Easier said than done, unfortunately. I have never had a shutdown while I was actually using the computer (is this a clue?), and I'm away from it for extended periods of time.

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Answer 4

Jul 14, 2015 9:50 AM in response to Linc Davis

Thanks for the instructions, but the clipboard is sadly empty :-(

Just to be sure, I removed the " | pbcopy " from the command (which I assume routes output to the clipboard), and ran it, and there was nothing output to the Terminal window.

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Answer 5

Linc Davis

Level 10

209,547 points

Jul 14, 2015 10:14 AM in response to G Robert Lewis

Make sure you haven't scheduled a shutdown in the Energy Saver preference pane.

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Answer 6

Jul 14, 2015 11:15 AM in response to Linc Davis

I have it set to shut down when the UPS has been in use for 5 minutes, or when its battery goes below 25%. But as I mentioned, the "outages" that happen once or twice a day (and which appear to maybe be UPS self-tests) only last for a couple of seconds.

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Answer 7

Linc Davis

Level 10

209,547 points

Jul 14, 2015 12:32 PM in response to G Robert Lewis

That's not what I'm referring to. Click the Schedule button.

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Answer 8

Jul 14, 2015 3:33 PM in response to Linc Davis

I have "Start up or wake weekdays at 02:25", but I never turn the system off.

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Answer 9

Linc Davis

Level 10

209,547 points

Jul 14, 2015 4:29 PM in response to G Robert Lewis

Resetting the System Management Controller (SMC) on your Mac - Apple Support

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Answer 10

Jul 14, 2015 7:11 PM in response to Linc Davis

Sorry, forgot to mention: resetting the SMC was the first thing I tried. No effect.

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Answer 11

Linc Davis

Level 10

209,547 points

Jul 14, 2015 7:18 PM in response to G Robert Lewis

Disconnect the USB cable from the UPS and see whether the shutdowns stop. If they don't, see below.

Make a "Genius" a ppointment at an Apple Store, or go to another authorized service provider. You may have to leave the machine there for several days.

Back up all data on the internal drive(s) before you hand over your computer to anyone. There are ways to back up a computer that isn't fully functional—ask if you need guidance.

If privacy is a concern, erase the data partition(s) with the option to write zeros* (do this only if you have at least two complete, independent backups, and you know how to restore to an empty drive from any of them.) Don’t erase the recovery partition, if present.

Keeping your confidential data secure during hardware repair

Apple also recommends that you deauthorize a device in the iTunes Store before having it serviced.

*An SSD doesn't need to be zeroed.

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Answer 12

Jul 16, 2015 8:54 AM in response to Linc Davis

OK, I think I may have figured out what's going on. Still awaiting confirmation, but here's the hypothesis:

I mentioned that the UPS has apparently done a brief self-test once or twice a day since it was new. I think what may be happening is that its battery recently got so weak that it can't even provide backup power for the few seconds that this operation takes. So power to the computer blips off and it suffers a rude shutdown.

I've replaced the UPS with a different one, and so far no shutdowns.

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Answer 13

Jul 23, 2015 9:55 AM in response to G Robert Lewis

After several days of no shutdowns, I think my diagnosis was correct.

Final point: Tripp-Lite denies that the UPS does these brief switches to backup power as self-tests, saying that there must be something about my AC power that's causing the UPS to detect power failure. Maybe so, but I've owned quite a variety of UPS's over the years, all plugged into the same AC line (which normally runs at 123–124VAC in my neighborhood), and this is the only one that's ever done this. Maybe it's just hypersensitive to tiny sags in the line voltage.

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